By Jon Frandsen, Senior Editor April 14, 2009 A predictable dispute is breaking out over whether the legalization of gay marriage in Iowa and Vermont portends a dramatic shift in the battle. Gay rights forces certainly have plenty to cheer about, but are they right, as they like to argue, that same sex marriage in America is inevitable?If they mean inevitable as in within a few decades, they may be right. But if they mean within a few years, they need to consider the slow pace in which political, judicial and public opinion tends to change.While no one can dispute the importance of the changes in Iowa and Vermont, there is plenty of disagreement over the broader significance. Take polls on gay marriage and civil unions. They vary widely depending upon how questions are phrased and what, exactly, is being asked. But generally opponents of gay marriage out poll supporters by 10-15 percentage points -- 55%-39% in a Newsweek poll in December last year and 55%-44% in a CNN poll the same month, for example. But when asked whether gay couples should be granted civil unions that give them most of the same rights of a married couple, those numbers flip-flop, clearly a sign that the public is generally sympathetic to the rights of homosexual couples but queasy about same-sex marriage. Some opponents to gay marriage argue that the poll numbers have been essentially static for a number years and support for same-sex marriage is not growing. Gay rights advocates, encouraged by the feeling that the American comfort-zone on the issue is growing, don't seem concerned by that argument. They see a number of other factors, including the judicial system, on their side.It's worth noting that courts often are far ahead of the public on some issues. In 1967, the year that the Supreme Court struck down bans on interracial marriage, some 72% of Americans opposed mixed race marriages. It wasn't until 1991 that opponents of those marriages dropped into the minority. That's a cheery statistic -- and a much cited one -- for backers of gay rights. But it does ignore a very salient fact: This Supreme Court today is far more conservative than the liberal Warren Court of the 1960s. For that reason and many other social, political and strategic factors, it may be a long time before the issue of gay marriage gets to -- and is accepted by -- the highest court in the land. So what does "inevitable" mean in terms of time? Well, first, inevitable is a bad word when it comes to politics and public opinion -- attitudes shift and weave over time and can go down as well as up. Remember, support for same sex marriage dropped (read comments of Pew Research Center's Scott Keeter) after the Masachusetts Supreme Court cleared the way in 2003 for it to became the first state in the country to permit them. More than any other factor, the real determinant could be demographics. Nate Silver, a polling expert who runs the astute blog www.fivethirtyeight.com (and who argues with careful numbers that support for gay marriage and civil unions is growing, but slowly), points out an important characteristic of most polling on the issue: Support for gay marriage and opposition to it is generational. He cites a CBS news poll in March that shows 64% of voters aged 18-45 supported either gay marriage or civil unions, but only 45 percent of voters aged 65 and up did. From there, the math is easy, at least for Silver: "Civil unions have already achieved the support of an outright majority of Americans, and as those older voters are replaced by younger ones, the smart money is that gay marriage will reach majority status too at some point in the 2010s."